PEST MANAGEMENT: WEEDS Use of Imazosulfuron in Arkansas Rice

Imazosulfuron is a new herbicide recently labeled in drilland water-seeded rice under the trade name LeagueTM. Research was conducted to understand the best fit for imazosulfuron in Arkansas rice culture, prior to its anticipated launch in 2011. Specifically, research was conducted (a) to understand the influence of application rate and timing on control, (b) to evaluate the effectiveness of imazosulfuron-containing herbicide programs relative to a standard herbicide program, and (c) to determine the rate of dissipation of imazosulfuron in drill-seeded rice. Imazosulfuron at 0.2 lb ai/acre provided no control of barnyardgrass and broadleaf signalgrass regardless of application timing but was effective in controlling yellow nutsedge and hemp sesbania when applied postemergence (POST). Imazosulfuron did not antagonize any of the herbicides with which it was mixed. As a result, herbicide programs containing imazosulfuron resulted in effective late-season control of barnyardgrass, hemp sesbania, and yellow nutsedge comparable to a current standard program. The half-life of imazosulfuron in soil appeared to differ according to soil pH, ranging from 3.2 days to 11.8 days, with the greatest persistence on an alkaline soil (pH = 7.4). As a result of the rapid dissipation of imazosulfuron in acidic soils, the residual activity of the herbicide may be relatively short lived.